Recovery of nickel and copper from sulfides

ABSTRACT

The present invention is directed to the treatment of sulfide materials containing nickel and/or copper sulfide but substantially free of iron to recover the metal values as a sulfate solution and to liberate elemental sulfur wherein the metal sulfide is slurried in an aqueous sulfuric acid-iron sulfate leach solution and is then heated at a temperature range of about 80* C. to 150* C. under an oxygen partial pressure of at least about 2 atmospheres to dissolve the metal values and liberate elemental sulfur.

United States Patent Inventors Charles Edward ONeill Oakville, Ontario;Alexander Illis, Mississaugua, Ontario; David Anthony Huggins,Mississaugua, Ontario, all of Canada App]. No. 835,797

Filed June 23, 1969 Patented Oct. 26, 1971 Assignee The InternationalNickel Company, Inc.

New York, N .Y.

Priority Aug. 3, 1968 Canada 026,644

RECOVERY OF NICKEL AND COPPER FROM SULF IDES 22 Claims, No Drawings U.S.Cl 204/ 108, 23/125, 75/82, 75/101, 204/109,204/1l2, 204/128 1nt.C1 C22d1/10,

C22b 23/06, C22b 3/00 501 Field of Search 75/82, 101; 23/l25;204/l08,109,112,128

[56] References Cited UNITED STATES PATENTS 3,004,846 10/1961 Queneau75/82 1,841,438 1/1932 Greenawalt 204/108 Primary Examiner-John H. MackAssistant Examiner-R. L. Andrews Attarney- Maurice L, Pinel ABSTRACT:The present invention is directed to the treatment of sulfide materialscontaining nickel and/or copper sulflde but substantially free of ironto recover the metal values as a sulfate solution and to liberateelemental sulfur wherein the metal sulfide is slurried in an aqueoussulfuric acid-iron sulfate leach solution and is then heated at atemperature range of about 80 C. to 150 C. under an oxygen partialpressure of at least about 2 atmospheres to dissolve the metal valuesand liberate elemental sulfur.

RECOVERY OF NICKEL AND COPPER FROM SULFIDES The present inventionrelates to an improved process for treating materials containing nickel,copper and sulfur to recover each of these elements and moreparticularly to the recovery of nickel, copper and sulfur from ores, oreconcentrates and metallurgical intennediates and crudes by a combinationof pyrometallurgical and hydrometallurgical processes andvapometallurgical processes for high nickelcontaining materials.

Ores, ore concentrates and metallurgical intermediates and crudescontaining nickel, copper and sulfur have been and are being treated bypyrometallurgical, hydrometallurgical, vapometallurgical andelectrochemical processes to recover nickel, copper and sulfur incommercial forms. Such prior processes also endeavored to provide aconcentrate of precious metals, if present in the starting material, inorder to facilitate the recovery of such precious metals. Although suchprior and existing processes were and are effective in recoveringnickel, copper, sulfur and the precious metals from the startingmaterials, such processes often entail large capital outlays, high laborcosts and incomplete or ineffective recovery of one or the other valuesfrom the starting material. For example, the pyrometallurgical treatmentof sulfide ores or ore concentrates containing nickel, cobalt, copperand the precious metals frequently involves the recirculation ofuneconomically large quantities of slag or other smelter intermediatesin order to insure high recoveries of metal values therefrom. A furtherexample is the hydrometallurgical treatment of such materials whichoften involves the nonselective dissolution of nickel and copper suchthat the separation and recovery of the metal values are rendereddifficult and expensive. Although attempts were made to overcome theforegoing difficulties and other disadvantages, none, as far as we areaware, was entirely successful when carried into practice commerciallyon an industrial scale.

It has now been discovered that sulfides of nickel and/or copper can behydrometallurgically treated to provide solutions from which nickeland/or copper can be recovered and to produce elemental sulfur. Thisdiscovery is particularly applicable to integrated processes forrecovering nickel and copper from ores, ore concentrates andmetallurgical crudes and intermediates.

It is an object of the present invention to provide a process forhydrometallurgically treating nickel and/or copper sulfides to producenickel and/or copper solutions and elemental sulfur.

it is an object of the present invention to provide a process forhydrometallurgically treating nickel and/or copper sulfides to producenickel and/or copper solutions and elemental sulfur.

It is a further object of the invention to provide an integrated processfor recovering nickel, copper and sulfur from materials containing thesame.

It is also an object of the present invention to recover precious metalsassociated with nickel and/or copper sulfides.

It is an object of the present invention to provide a process forrecovering nickel, copper and sulfur from starting materials containingthe same by a combination of pyrometallurgical and hydrometallurgicalprocesses.

Generally speaking, the present invention contemplates a process fortreating substantially iron-free sulfides of at least one metal selectedfrom the group consisting of nickel and copper to produce a sulfatesolution of the metal and to liberate elemental sulfur. The metalsulfide, in finely divided form, is slurried in an aqueous solution,which solution contains at least about 2 grams per liter (g.p.l.) ironas iron sulfate and sulfuric acid at least in stoichiometric amounts tocombine with the metal in the sulfide. The slurry is heated to atemperature between about 80 C. and 150 C. under an oxygen partialpressure of at least about 2 atmospheres (atm) to form a sulfatesolution of the metal and to liberate elemental sulfur. lt isadvantageous to recover the metal from solution by electrolytictechniques so that sulfuric acid solution containing the iron can beregenerated and returned to the leaching operation.

The process of the present invention is advantageously employed inconjunction with prior processing techniques. A particularlyadvantageous embodiment of an integrated process involves the treatmentof ores, ore concentrates and metallurgical crudes and intermediateswhich contain sulfur and at least one metal selected from the groupconsisting of nickel and copper by pyrometallurgical and/orvapometallurgical techniques which produce sulfide intermediate productsof nickel and/or copper. As will be described hereinafter, suchmaterials, either out of necessity or by design, are treated to removeiron so that in most instances the sulfide to be treated in accordancewith the present invention will be substantially iron-free, i.e., thesulfide will contain no more than about 1 percent or 1.5 percent ironand advantageously no more than about 0.5 percent iron. An example ofsuch an integrated process comprises providing a starting material in adrastically quenched state which contains copper and sulfur in amountsso that the copper to sulfur ratio is between about 3.5: l or 4: l and10:1, nickel and controlled amounts or iron. The starting material isleached with an acidic aqueous solution containing copper sulfate inamounts at least stoichiometrically equivalent to the nickel, iron andcobalt contained in the starting material and sufficient sulfuric acidto maintain a pH value below about 5. Advantageously, the copper sulfatesolution contains a stoichiometric excess of copper sulfate of up toabout 20 percent in order to insure maximum dissolution of the nickel,iron and cobalt as sulfates. This leaching operation is conducted at atemperature between about C. and 250 C. under the pressures generated atthese temperatures The residue obtained from this leaching operationcontains substantially all the copper in the starting material as coppersulfide and cement copper and is substantially free of iron. Afterfiltration, the filtrate is treated to recover nickel and the residue istreated to recover copper and sulfur. The coppercontaining residue isleached with an acidic aqueous solution, which contains at least about 2g.p.l. iron as iron sulfate and sulfuric acid in amounts of at leastabout the stoichiometric equivalent to the copper contained in thecopper per residue (advantageously a stoichiometric excess of up toabout 20 percent is employed), at a temperature between about 80 C. andC. and at oxygen partial pressures between about 2 atm. and 20 atm. todissolve substantially all the copper in the residue as copper sulfateand to liberate elemental sulfur The copper sulfate solution is treatedto recover copper. When the starting materials contain precious metals,the precious metals will be associated with the elemental sulfur and arerecovered therefrom. The oxidative leaching operation will be describedhereinafter in conjunction with the treatment of materials containingnickel, copper and sulfur in order to recover each of these elements.

Any nickeland copper-containing material can be treated in accordancewith the integrated process of the present invention. Thus, ores, oreconcentrates and metallurgical intermediates and crudes, which containnickel, copper and sulfur, can be treated by the process disclosedherein. Such materials can also contain cobalt and the precious metalswhich are also recovered. The terms "metallurgical intermediates" andmetallurgical crudes" include materials such as mattes, metal anodesludges, sulfide anode sludges, carbonyl residues, sulfided scrap andmatte separation products. The starting material will generally havenickel to copper ratios between about l00:l and 1:25. Materials havinglower nickel to copper ratios can be treated by conventional copperpractice.

When separating nickel from copper, either by leaching or by acombination of vapometallurgical techniques and leaching, the ironcontent in the starting material is controlled to be below about 2percent, advantageously the iron content is lowered to less than about0.5 percent. Lowering of the iron content to these limits is extremelyimportant in providing efficient low-cost recovery of nickel and copperwhether the initial separation is by the first stage leaching with thecopper sulfate solution or by initial separation by vapometallurgicaltechniques as described hereinafter followed by a like leachingoperation of the vapometallurgical residue. The starting material, ifprimarily sulfide in form, is smelted and treated with afree-oxygen-containing gas, e.g., air, oxygen-enriched air or commercialoxygen, to oxidize and remove substantially all the iron. The treatmentwith the free-oxygen-enriched air or commercial oxygen, to oxidize andremove substantially all the iron. The treatment with thefree-oxygen-containing gas is continued to provide a molten bath withcopper to sulfur ratios of at least about 3.5:l, advantageously thecopper to sulfur ratio is controlled to be between about 4:1 and :1, andthe molten bath is then drastically quenched by techniques such asshotting or granulation When the starting material contains sulfur inamounts insufficient to provide the aforementioned copper to sulfurratios, the material can. be melted and treated with afree-oxygen-containing gas to lower the iron content to below about 2percent before adding a sulfurbearing material to provide the desiredcopper to sulfur ratio or the sulfur-bearing material can be added priorto the treatment with the free-oxygen-containing gas.

When separating nickel from copper, as noted hereinbefore, the copper tosulfur ratio of starting material is pyrometallurgically adjusted tobetween about 4:1 and 10: l.

Thus, it is seen that after the pyrometallurgical treatment the sulfurcontent of the bath is, in most instances, insufficient to fon'nsizeable amounts of nickel sulfide upon solidification. This is anadvantageous feature of the present invention since separation of nickelfrom copper is greatly enhanced by the presence of metallic nickelrather than nickel sulfide. However, the molten nickel-copper bath withthe controlled sulfur content is advantageously drastically quenched inorder to take full advantage of the controlled sulfur content. Theinstantaneous solidification obtained by drastic quenching insuressubstantially homogenous distribution of the sulfur throughoutsolidified material. Such uniform sulfur distribution promotes rapid andhighly selective separation of nickel from copper by bothhydrometallurgical and vapometallurgical techniques.

Whatever the nickel to copper ratio is in the drastically quenchedmaterial, it can be treated with an acid aqueous solution, whichcontains copper sulfate in amounts at least about stoichiometricallyequivalent to the nickel, iron and cobalt contained in the startingmaterial and sulfuric acid in amounts sufficient to maintain thesolution at a pH below about 5, at a temperature between about 100 C.and 250 C. under the pressures generated at the correspondingtemperatures to dissolve substantially all the nickel, cobalt and ironas sulfates and to provide a residue containing substantially all thecopper both from the drastically quenched material and from the aqueoussolution. Advantageously, the acidic aqueous solution contains coppersulfate in an excess amount of up to about percent, e.g., about 10percent, of the stoichiometric amount required to react with the nickel,iron and any cobalt contained in the solid and sulfuric acid in amountssufficient to maintain the solution at a pH value between about i and 2so that substantially all the copper in solution is cemented out orprecipitated as copper sulfide while substantially all the nickel, ironand cobalt are brought into solution. it is to be noted that thisleaching operation is conducted without any intentionally createdpartial pressure of oxygen other than the oxygen in the air entrapped inthe leaching apparatus, e.g., an autoclave. The leaching conditions aresuch that in the absence of any artificially created oxygen partialpressures any iron present tends to go into solution with the nickel.Such iron is undesirable for at least two reasons. Firstly, thenickel-containing solution must be freed of the dissolved iron in orderto obtain a purified nickel product, and secondly, as more iron goesinto solution greater quantities of chemicals and larger capacityequipment are required. For the foregoing reasons it is essential toinitially treat the starting material to lower the iron content to lessthan about 2 percent.

Although starting materials having nickel to copper ratios of as high asabout l00:l can be, after iron and sulfur adjustment and drasticquenching, treated by leaching to provide a nickel solutionsubstantially free of copper, it is advantageous to treat thedrastically quenched material by vapometallurgical techniques when thenickel to copper ratio exceeds about 1:2, advantageously nickel tocopper ratios of about lzl or even higher. The vapometallurgicaltreatment comprises carbonylating the drastically quenched material withcarbon monoxide partial pressures of at least about 5 atms. but lessthan about 100 atms. at a temperature between about 50 C. and 200 C. toform substantially pure nickel carbonyl. Higher and lower partialpressures of carbon monoxide can be employed but higher pressuresrequire much heavier equipment with concomitant higher capitalexpenditures while lower pressures result in slower and less completecarbonylation. Advantageously, carbon monoxide partial pressures ofbetween about 10 atms. and 60 atms. are employed to insure rapid andcomplete carbonylation while avoiding the use of heavier equipment.Control of the sulfur and iron contents and drastic quenching of amolten bath of such controlled composition is of the utmost importancewhen the carbonylation treatment is employed to effect an initialseparation of nickel from copper. Control of the sulfur content anddrastic quenching to uniformly distribute the sulfur provides an activemetal product for carbonylation. If the drastically quenched materia1contains above about 2 percent iron, the recovery of nickel as nickelcarbonyl rapidly falls to a point when the carbonylation treatment isrendered uneconomic. Starting materials, which have been drasticallyquenched and which have nickel to copper ratios of more than about l:lcopper to sulfur ratios of between about 4:1 and l0:l and less thanabout 2 percent iron, can be treated under the foregoing carbonylationconditions to provide nickel recoveries as substantially pure nickelcarbonyl of more than about percent, e.g., nickel recoveries of aboutpercent to percent. The residue from the carbonylation treatment, whichcontains substantially all the copper, cobalt and sulfur from thedrastically quenched material, is then treated by the first stageleaching operation under the conditions specified hereinbefore.

The residue from the first stage leaching operation is subjected to anoxidative leaching treatment to dissolve substantially all the copper ascopper sulfate and to liberate elemental sulfur, which is a preferredcommercial form of sulfur. The oxidative leaching treatment with alixiviant, which contains at least about 2 g.p.l. of iron as ironsulfate and sulfuric acid in amounts at least stoichiometricallyequivalent to the copper in the residue, is advantageously conducted inan autoclave at a temperature between about C. and C. with partialpressures of oxygen between about 5 atms. and 15 atms. Advantageously,sulfuric acid is employed in excess stoichiometric amounts of up toabout 20 percent, e.g., about 10 percent. The iron content in the acidicaqueous solution is advantageously controlled to provide ironconcentrations between about 4 g.p.l. and 10 g.p.l. At lower ironconcentrations the rate of reaction is quite low and, as the ironconcentration increases, the reaction proceeds much more rapidly.However, it is preferred to limit the iron concentration to below about10 g.p.l., in order to minimize the difficulties encountered by thepresence of iron in the pregnant copper sulfate solution when recoveringcopper therefrom, whether by electrolytic means, hydroxide or carbonateprecipitation or precipitation by hydrogen reduction. An importantfeature of the present invention is to provide an iron concentration ofat least about 2 g.p.l., which can be either in the ferrous or ferricstage since under the oxidative leaching conditions ferrous iron will beoxidized to ferric iron, in order to insure the liberation of elementalsulfur. The prior art has not recognized the importance of providingferric ions during the oxidative leaching of nonferrous sulfides inorder to produce elemental sulfur. For example, copper sulfide whenslurried with stoichiometric amounts of sulfuric acid in a glass-linedstainless steel autoclave and heated to a temperature of ll0 C. with anoxygen partial pressure of 10 atm. produced only a copper sulfatesolution and no elemental sulfur whereas copper sulfide slurried withstoichiometric amounts of sulfuric acid and 5 g.p.lfofferr icironproduced a copper tfirlfate solution and liberated over 90 percent ofthe sulfur in the copper sulfide as elemental sulfur. The initial stagesof the oxidative leaching operation are advantageously conducted attemperatures of about 110 C. since at higher temperatures the liberatedelemental sulfur melts and wets, i.e., coats, the copper residue therebyhindering the leaching action of the solvent. When the starting materialcontains precious metals, i.e., gold, silver, and the platinum groupmetals, the precious metals will follow the copper residues up tooxidative leaching operation where the precious metals ultimately reportin the elemental sulfur-containing residue.

The precious metals associated with the elemental sulfur can be furtherconcentrated by melting and filtration. Elemental sulfur adhering to theprecious metal concentrate can be burned off as sulfur dioxide in afree-oxygen-containing gas. The precious metal concentrate is thentreated by conventional means such as sulfation with sulfuric acid tosolubilize base metals such as copper so that upon leaching an even moreconcentrated precious metal residue is obtained which can be treated byrecognized means to individually recover each of the precious metalspresent. Advantageously, sulfation. of the precious metal concentrate isconducted at a temperature below about 170 C.

Another example of the use of the process in accordance with the presentinvention in conjunction with prior processing is the treatment of thecopper-rich fraction obtained by slowly cooling a nickel-copper matte.Although the separation of nickel from copper by the matte separationprocess is highly selective, particularly insofar as the nickelrichfraction is concerned, the copper-rich fraction frequently contains upto about percent nickel. The copper-rich fraction is advantageouslytreated with a copper sulfate solution, as described hereinbefore, toproduce a copper sulfide residue and a nickel sulfate solution fromwhich nickel is recovered. The copper sulfide residue is then slurriedwith an acidic aqueous solution containing iron as iron sulfate in anamount of at least about 2 g.p.l. and sulfuric acid in an amount atleast stoichiometrically equivalent to the copper in the copper sulfideresidue. The slurry is heated to a temperature between about 80 C. and125 C. under an oxygen partial pressure of at least about 2 atmospheres,e.g., about 5 atmospheres or higher, to produce elemental sulfur and apregnant copper sulfate solution which can be treated to recover copper.Advantageously, a portion of the pregnant copper sulfate solution isrecycled to the first stage leaching operation in amounts such that thecopper in the pregnant solution is at least stoichiometricallyequivalent to the nickel contained in the copper-rich fraction and theremainder of the pregnant copper sulfate solution is treated for copperrecovery before recycling it to the second stage leaching operation.

The pregnant copper sulfate solution from the oxidative leaching istreated for recovery of copper. Advantageously, a portion of thepregnant copper sulfate solution is recycled to the first leachingoperation in amounts such that copper sulfate requirements of the firststage leaching solution are fulfilled while the remainder of thepregnant solution is treated for copper recovery. Copper can berecovered from the pregnant solution by cementation or by alkaliprecipitation, but such recovery techniques. entail further processingto recover copper in commercial forms or the addition of reagents. lt ispossible to recover the copper from the solution by electrowinning or byhydrogen reduction techniques. Advantageously, the copper is recoveredby electrowinning. The electrowinning of copper from solution isconducted so that about 40 percent to 80 percent, advantageously about60 percent to 70 percent, of the copper in solution is recovered aselectrolytic copper. The spent electrolyte advantageously contains about30 g.p.l. to 40 g.p.l. copper as cupric sulfate, about 4 g.p.l. to 10g.p.l. liter of iron as iron sulfate and about 150 g.p.l. free sulfuricacid. The spent electrolyte is recycled to the second stage leaching,i.e., oxidative leaching, operation. If

the iron concentration the spent electrolytgis in sufficient to providea ferric ion concentration in the second stage leaching operation toproduce elemental sulfur, additional iron can be added to the autoclave.The recirculation of the electrolyte to the oxidative leaching stageprovides a substantially closed circuit which eliminates the necessityof providing fresh lixiviants thereby substantially lowering waterrequirements and avoiding problems associated with water pollution.

The nickel sulfate solution obtained from the first stage leachingoperation is treated to recover nickel and cobalt in commerciallyacceptable forms. The nickel sulfate solution, which contains irondissolved from the starting material and from the iron contained in thepregnant solution from the second stage leaching operation, is firsttreated to eliminate iron. Iron can be removed from the solution asferric hydroxide by the addition of a base such as calcium hydroxidewhile oxidizing the solution with air. Of course, iron can be removed byany other known means. Copper, which is present in the nickel sulfatesolution due primarily to the use of excess stoichiometric amounts ofcopper sulfate in the first stage leaching operation, can be removedfrom the solution after iron removal by electrolytic means, hydrogensulfide precipitation, precipitation by selective hydrogen reduction orby ion exchange techniques including liquid-liquid extraction. If thenickel sulfate solution contains cobalt, cobalt is recovered byoxidation and precipitation with a base such as sodium hydroxide or byion exchange techniques. Advantageously, cobalt is first removed ascobaltic hydroxide, which after being redissolved in hydrochloric acidis treated by ion exchange processes to recover a pure form of cobalt.The thus-purified nickel sulfate solution can then be treated to recovernickel. For example, sodium carbonate is added to the solution toprecipitate nickel carbonate, which is usable as such or which can becalcined to nickel oxide.

For the purpose of giving those skilled in the art a betterunderstanding of the invention and/or a better appreciation of theadvantages of the invention, the following illustrative examples aregiven:

EXAMPLE I A nickel-copper matte having a nickel to copper ratio of 1251was blown to a copper to sulfur ratio of 3.7:l and was drasticallyquenched by granulation to provide a partially metallized material. Thegranulated metallized material was ground to pass through a 200 meshscreen (Tyler Series). Nickel, cobalt and iron were selectively leachedfrom the metallized material by metathesis as a slurry of 40 percentsolids by weight with an acidic aqueous solution of copper sulfate in aglass-lined stainless steel autoclave, which was provided with anagitator for increasing liquid-solid contact, for 2 hours at 200 C. Theacidic aqueous solution contained a stoichiometric excess of coppersulfate of more than 10 percent and sufficient sulfuric acid to maintainthe solution at a pH below 5. The results of the metathesis leaching aregiven in table I, and it is to be noted that the resulting residuecontained only 0.17 percent iron and substantially all the copper inboth the copper sulfate solution and the granulated matte and had acopper to sulfur ratio of about 4.4: l

After filtration, the residue was slurried with a second acidic aqueoussolution at 10 percent solids by weight. The acidic aqueous solutioncontained 150.2 g.p.l. sulfuric acid and 5.9 g.p.l. iron as iron sulfateand was a spent electrolyte from previous electrowinning of coppersulfate from an oxidative leach solution solution. The sulfuric acid wasmore than about 10 percent in excess of that amount stoichiometricallyrequired to react with the copper in the residue. The slurry was heatedto a temperature of C. under an oxygen partial pressure of IO atms. for1.5 hours in a glass-lined stainless steel autoclave, which was providedwith a stirrer to promote gas-liquid-solid contact. The results of thisoxidative leaching test are reported in table I. It will be noted that92 percent of the sulfur in the quenched matte was recovered aselemental sulfur.

7 7 TABiE 1 i Weight, Analysis wL/percent or gpl Distribution percentgrns. or Sample vol., ml. Cu Ni Co Fe Cu Ni Co Fe S Partially metallizedmaterial 100 67.1 13.2 0.24 0.46 18.0 100 100 100 CuSO. solution 15092.9 7.6 0.30 5.0 2 9.8 20.8 8.6 18.8 Metathesis leach residue. 99.979.4 0.55 0.04 0.17 18.0 118.2 4.2 17.0 Pregnant solution... 150 11.592.0 1.6 6.9 2 0.3 2.6 104.5 100 Barren electrolyte. 900 28.7 10.2 0.165.9 150.2 38.5 69.5 60.0 Final residue..... 14.2 8.3 0.08 0.01 0.11 189.9 2.3 0.1 0.8 Pregnant solution.. 900 114.7 10.7 0.20 6.1 2 14.2155.5 73.6 76.2

Solids are given in weight percent and solutions in grams per liter. 3gpl P1 504- 3 85.7% elemental sulfur. 92% as elemental sulfur.

EXAMPLE ll :5 rich fraction containin 5.88 ercent nickel was recovered bg P l A 1,500 pound lot of a material containing copper, nickel andsulfur was top blown in a rotary oxygen converter to a sulfur content of4.9 percent and was granulated. The drastically quenched productcontained 19.6 percent copper, 70.5 percent nickel, 1.96 percent iron,0.86 percent cobalt and 4.12 percent sulfur, e.g., a copper to sulfurratio of about 4.75:1. The drastically quenched product was carbonylatedunder a partial pressure of carbon monoxide of atmospheres to extract96.9 percent of the nickel as a substantially pure nickel carbonyl andto provide a carbonylation residue which contained substantially all thecopper, cobalt, iron and sulfur. Nickel, iron and cobalt wereselectively leached by metathesis with an acidic aqueous solution as aslurry of 25 percent solids at a temperature of 180 C. for 2 hours. Theacidic aqueous solution contained copper sulfate in a stoichiometricexcess of about 8 percent of that required to react with all the nickel,cobalt and iron in the carbonylation residue and sufficient sulfuricacid to maintain the pH below about 5. The residue from the metathesisleach, which contained copper and sulfur in a ratio of about 5.5:1, wassubjected to an oxidative leach to provide a pregnant copper sulfatesolution and to produce elemental sulfur. The oxidatlve leach wasaccomplished with a selective flotation. The copper-rich fraction had acopper to sulfur ratio of about 3.56 to 1. The nickel was selectivelyleached as a slurry of percent solids, by weight, with an acidic aqueoussolution at a temperature of 200 C. for 2 hours. The acidic aqueoussolution contained copper sulfate in an amount stoichiometrically inexcess of that required to react all the nickel, cobalt and ironcontained in the copperrich fraction and contained sufficient sulfuricacid to maintain the pH of the acidic aqueous solution below about 5.The metathesis leach produced a nickel sulfate solution and a residuecontaining substantially all the copper in the copperrich fraction andin the acidic aqueous solution. The metathesis leach residue wasslurried in a second acidic aqueous solu tion at 10 percent solids byweight. The second acidic aqueous solution contained 5.9 g.p.l. iron asiron sulfate and sulfuric acid in an amount stoichiometrically in excessof that required to react with all of the copper contained in themetathesis leach residue. The slurry was heated to a temperature of 105C. under an oxygen partial pressure of 10 atmospheres to produce apregnant copper sulfate and elemental sulfur. It will be noted that 90percent sulfur was recovered as elemental sulfur. The results of thisexample are reported in table 111.

TABLE 111 Analysis percent 1 Distribution percent Weight. Sample gms. CuNi (0 Fe 5 Cu Ni Co Fe 5 Copper-rich 100 70.3 5.88 0.088 0.58 19.7 100100 100 100 100 Metathesis leach residue 96 76.8 0.10 0.01 0.58 20.3 1041.6 1 1.0 96 99 Oxidative leach residue 19.2 4.3 0.08 0.01 0.11 2 94.01.2 0.25 2.2 3.6 92

' Solids are given in weight percent. 92.8% of which was elementalsulfur.

3 90% of the sulfur contained in copper-rich fraction was recovered aselemental sulfur.

slurry of about 10 percent solids by weight in an acidic aqueoussolution at a temperature of 105 C. under an oxygen par- It is to beobserved that the present invention provides a process for recovering atleast about 80 percent elemental sultial pressure of 10 atmospheres for1.5 hours. The acidic aquefor (advantageously more than about 90 percentand even up ous solution contained 5 grams per liter iron as ironsulfate to 100 percent from a substantially iron-free sulfide of a metaland sufficient sulfuric acid to react with at least all of the selectedfrom the group consisting of nickel and copper by oxcopper contained inthe metathesis leach residue. The results idatively leaching the sulfidewith an aqueous sulfuric acidof this example are reported in table 11-iron sulfate leach solution containing at least about 2 g.p.1.

TABLE 11 Weight, Assay percent or gpl Distribution percent grns. orSample vol., ml. Cu Ni Co Fe 5 Cu Ni Co Fe 5 Pressure carbonyl residue100 59-9 7.83 5.20 4.45 13.5 100 100 100 100 100 G050. solution 300 59.12.41 0.48 2.41 13.7 29.6 9.20 2.80 16.2 Leach residue... 96.7 77.6 0.430.09 1.17 14.0 125.9 5.39 1.7 25.4 100 Pregnant solution. 300 7.4 27.117.5 13.5 3.7 103.9 101.1 90.8 Dilute sulfuric acid.. 900 5.0 86.5 Finalresidue 16.2 2. 0.05 0.66 82.0 0.78 1.03 2.40 98.4 Pregnant solution 90082.7 0.07 5.4 124 4.28 0 109.5

Solids are given in weight percent and solutions in grams per liter. 1gpl H 50 iron and sulfuric acid at least stoichiometrically equivalentto A nickel-copper matte was slow 1y cooled and th e copperthe metal inthe sulfide and heating the metal sulfide and the acidic aqueoussolution to a temperature between about 80 'C. and 150 C.,advantageously between about 80 C. and

125 C. and even more advantageously between about 100 C. and 110 C.,under a partial pressure of oxygen of at least about 2 atrns. to providea metal sulfate solution and to liberate elemental sulfur. It is to beunderstood that the term substantially iron-free sulfide" as used hereinrefers to a sulfide that contains iron in insufficient amounts toprovide the required concentration of iron in the acidic aqueoussolution or a sulfide that contains iron in such a form that the ironwill not be brought into solution. Furthermore, it is to be understoodthat all percentages and ratios given herein are taken on a weight basisunless otherwise stated.

It is to be further observed that the process in accordance with thepresent invention can be employed to recover nickel, copper and sulfurfrom materials containing the same by employing a two-stage leachingprocess. The first stage leaching operation is accomplished bymetathesis with a copper sulfate solution in order to provide ametathesis leach solution containing nickel and a substantiallyiron-free metathesis leach residue containing substantially all thecopper in the starting material. The second stage leaching operation isan oxidative leaching operation which produces a pregnant copper sulfatesolution from which copper can be recovered and elemental sulfur. Nickelis recovered from the nickel-containing metathesis leach solution. Informing the slurry for the metathesis leach, the amount of solidsincorporated in the slurry is limited only by the capacity of theapparatus being employed. Most generally, the metathesis leach slurrywill contain between about 25 percent and 50 percent solids by weight.The slurry formed for the oxidative leaching operation will usuallycontain between about 5 percent and 25 percent solids by weight.

The process of the present invention is not to be confused with priorprocesses which employ oxidative leaching since such prior processes didnot teach the necessity of providing a minimum concentration of iron insolution together with controlled amounts of sulfuric acid to produceelemental sulfur from substantially iron-free nickel and/or coppersulfides. For example, McKechnie at a very early date employed oxidativeleaching techniques in treating nickeland/or copper-containing sulfidematerials but did not disclose the necessity of employing both aniron-containing and sulfuric acid containing leach solution. At a muchlater date, Forward, Nashner, Mc- Gauley and others employed oxidativeleaching techniques for treating both ferrous and nonferrous materials.These later workers did not appreciate the necessity of providing bothiron in solution and sulfuric acid in controlled amounts when treatingsubstantially iron-free sulfides of copper and nickel to produceelemental sulfur.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A process for treating substantially iron free sulfides of at leastone metal selected from the group consisting of nickel and copper toproduce a sulfate solution of the metal and to liberate elemental sulfurwhich comprises slurrying the metal sulfide in an aqueous sulfuricacid-iron sulfate leach solution containing at least about 2 g.p.l. ironand sulfuric acid at least stoichiometrically equivalent to the metal inthe sulfide and heating the slurry to a temperature between about 80 C.and 150 C. under an oxygen partial pressure of at least about 2 atrns.to form a pregnant sulfate solution of the metal and to liberateelemental sulfur.

2. A process as described in claim 1 wherein the metal sulfide is copperand copper is recovered from the pregnant sulfate solution byelectrowinning.

3. A process as described in claim 2 wherein the electrowinningtreatment produces a spent electrolyte which is recycled to form theacidic aqueous leach solution.

4. A process as described in claim 1 wherein an oxygen partial pressureof at least about 5 atrns. is employed.

5 A process as described in claim 1 wherein sulfuric acid is employed inexcess stoichiometric amounts of up to about 20 percent.

6. A process as described in claim 1 wherein copper is recovered fromthe pregnant copper sulfate solution by cementation.

7. A process as described in claim 1 wherein copper is recovered fromthe pregnant copper sulfate solution by alkali precipitation.

8. A process as described in claim i wherein copper is recovered fromthe pregnant copper sulfate solution by hydrogen reduction.

9. A process for recovering copper, nickel and sulfur from materialscontaining the same which comprises providing a starting material in thegranulated, drastically quenched state and having a coppercsulfur ratiobetween about 3.5:1 and 10:1; slurrying the starting material in finelydivided form with an acidic aqueous solution, which solution containscopper sulfate in amounts at least stoichiometrically equivalent to thenickel contained in the starting material and sufficient sulfuric acidto maintain the solution at a pH value below about 5; heating the slurryto a temperature between about C. and 250 C. under pressures generatedat these temperatures to leach nickel from the starting material bymetathesis to thereby produce a metathesis leach solution containingnickel and a metathesis-leach residue containing substantially all thecopper in the starting materials; recovering nickel from themetathesis-leach solution; slurrying the metathesis-leach residue withan acidic aqueous solution, an aqueous sulfuric acid-iron sulfate leachsolution containing at least about 2 g.p.l. iron and sulfuric acid atleast stoichiometrically equivalent to the copper in themetathesis-leach residue; heating the metathesis-leach-residue slurry toa temperature between about 80 C. and 150 C. under an oxygen partialpressure of at least about 2 atms. to form a pregnant copper sulfatesolution and to liberate elemental sulfur; and recovering copper fromthe pregnant copper sulfate solution.

10. A process as described in claim 9 wherein the starting materialcontains cobalt and the precious metals, and the cobalt is recovered inthe metathesis-leach solution containing nickel while the preciousmetals are recovered from the elemental sulfur. H

11. A process as described in claim 9 wherein copper is recovered fromthe pregnant copper sulfate solution by electrowinning whereby a spentelectrolyte is produced which spent electrolyte is employed in formingthe slurry with the metathesis leach residue.

12. A process as described in claim 9 wherein a portion of the pregnantcopper sulfate solution is employed in forming the slurry used inmetathesis leach.

13. A process as described in claim 9 wherein a portion of the pregnantcopper sulfate solution is recycled to the metathesis leach insufficient quantities to satisfy the stoichiometric copper sulfaterequirements.

14. A process as described in claim 9 wherein copper is recovered byelectrowinning, and the resulting spent electrolyte is employed informing the metathesis leach residue slurry.

15. A process as described in claim 9 wherein the aqueous sulfuricacid-iron sulfate leach solution contains between about 4 g.p.l. an 10g.p.l. iron.

16. A process as described in claim 9 wherein an oxygen partial pressurebetween about 2 atrns. and 20 atrns. is employed.

17. A process as described in claim 9 wherein themetathesis-leach-residue slurry is heated to a temperature between about80C. and C.

18. A process as desciibedi n claim 9 wheiitinthe r rietathesis-leach-residue slurry is heated to a temperature between about100C. and 110 C.

atms. A process as described in claim 9 wherein oxygen, partialpressures of at least about atms. are employed.

20. A process for recovering nickel, copper and sulfur from materialscontaining the same which comprises providing a starting material in thedrastically quenched state and having a nickel to copper ratio greaterthan about 1:2 and a copper to sulfur ratio greater than about 4:1;treating the drastically quenched material with carbon monoxide partialpressures at least about 5 atms. and less than about 100 atms. at atemperature between about 50 C. and 200 C. to form substantially purenickel carbonyl and to provide a carbonylation residue; fonning a slurryof the carbonylation residue with an acidic aqueous solution, whichsolution contains copper sulfate in amounts at least aboutstoichiometrically equivalent to the nickel contained in thecarbonylation residue and sulfuric acid in amounts sufficient tomaintain the solution at a pH value below about 5; heating thecarbonylation residue slurry to a temperature between about 100 C. and250 C. to leach the nickel therefrom by metathesis, to thereby produce ametathesis-leach solution containing nickel and ametathesis-leachresidue containing substantially all the copper;recovering nickel from the metathesis-leach solution; forming a slurryof the metathesis-leach-residue with an aqueous sulfuric acidironsulfate leach solution containing at least about 2 g.p.l. iron andsulfuric acid at least stoichiometrically equivalent to the copper inthe metathesis-leach-residue; heating the nietath esisJeach-res idiieslurry to a temperature between about 80 C. and 150 C. under oxygenpartial pressures of at least about 2 atms. to produce a pregnant coppersulfate solution and to liberate elemental sulfur and recovering copperfrom the pregnant copper sulfates.

21. A process for treating a copper-rich fraction of copper sulfideobtained from a slowly cooled nickel-copper matte to recover copper,nickel and sulfur which comprises forming a slurry of the copper-richfraction with an acidic aqueous solution, which solution contains coppersulfate in amounts at least about stoichiometrically equivalent to thenickel contained in the copper-rich fraction and sufficient sulfuricacid to maintain the solution at a pH value below about 5; heating thecopper-rich slurry to a temperature between about C. and 250 C. to leachnickel from the copper-rich fraction by metathesis to thereby produce ametathesis-leach solution containing nickel and ametathesis-leach-residue containing substantially all the copper;recovering nickel from the metathesis leach solution; forming a slurryof the metathesisleach-residue with an aqueous sulfuric acid-ironsulfate leach solution containing at least about 2 g.p.l. iron andsulfuric acid at least stoichiometrically equivalent to the copper inthe metathesis-leach-residue; heating the metathesis-leachresidue slurryto a temperature between about 80 C. and C. under oxygen partialpressures of at least about two atmospheres to produce a pregnant coppersulfate solution and to liberate elemental sulfur; and recovering copperfrom the pregnant copper sulfates.

22. A process as described in claim 21 wherein the copperrich fractioncontains cobalt and the precious metals, and cobalt is recovered fromthe metathesis-leach solution containing nickel while the preciousmetals are recovered from the elemental sulfur.

2. A process as described in claim 1 wherein the metal sulfide is copperand copper is recovered from the pregnant sulfAte solution byelectrowinning.
 3. A process as described in claim 2 wherein theelectrowinning treatment produces a spent electrolyte which is recycledto form the acidic aqueous leach solution.
 4. A process as described inclaim 1 wherein an oxygen partial pressure of at least about 5 atms. isemployed. 5 A process as described in claim 1 wherein sulfuric acid isemployed in excess stoichiometric amounts of up to about 20 percent. 6.A process as described in claim 1 wherein copper is recovered from thepregnant copper sulfate solution by cementation.
 7. A process asdescribed in claim 1 wherein copper is recovered from the pregnantcopper sulfate solution by alkali precipitation.
 8. A process asdescribed in claim 1 wherein copper is recovered from the pregnantcopper sulfate solution by hydrogen reduction.
 9. A process forrecovering copper, nickel and sulfur from materials containing the samewhich comprises providing a starting material in the granulated,drastically quenched state and having a copper:sulfur ratio betweenabout 3.5:1 and 10:1; slurrying the starting material in finely dividedform with an acidic aqueous solution, which solution contains coppersulfate in amounts at least stoichiometrically equivalent to the nickelcontained in the starting material and sufficient sulfuric acid tomaintain the solution at a pH value below about 5; heating the slurry toa temperature between about 100* C. and 250* C. under pressuresgenerated at these temperatures to leach nickel from the startingmaterial by metathesis to thereby produce a metathesis leach solutioncontaining nickel and a metathesis-leach residue containingsubstantially all the copper in the starting materials; recoveringnickel from the metathesis-leach solution; slurrying themetathesis-leach residue with an acidic aqueous solution, an aqueoussulfuric acid-iron sulfate leach solution containing at least about 2g.p.l. iron and sulfuric acid at least stoichiometrically equivalent tothe copper in the metathesis-leach residue; heating themetathesis-leach-residue slurry to a temperature between about 80* C.and 150* C. under an oxygen partial pressure of at least about 2 atms.to form a pregnant copper sulfate solution and to liberate elementalsulfur; and recovering copper from the pregnant copper sulfate solution.10. A process as described in claim 9 wherein the starting materialcontains cobalt and the precious metals, and the cobalt is recovered inthe metathesis-leach solution containing nickel while the preciousmetals are recovered from the elemental sulfur.
 11. A process asdescribed in claim 9 wherein copper is recovered from the pregnantcopper sulfate solution by electrowinning whereby a spent electrolyte isproduced which spent electrolyte is employed in forming the slurry withthe metathesis leach residue.
 12. A process as described in claim 9wherein a portion of the pregnant copper sulfate solution is employed informing the slurry used in metathesis leach.
 13. A process as describedin claim 9 wherein a portion of the pregnant copper sulfate solution isrecycled to the metathesis leach in sufficient quantities to satisfy thestoichiometric copper sulfate requirements.
 14. A process as describedin claim 9 wherein copper is recovered by electrowinning, and theresulting spent electrolyte is employed in forming the metathesis leachresidue slurry.
 15. A process as described in claim 9 wherein theaqueous sulfuric acid-iron sulfate leach solution contains between about4 g.p.l. an 10 g.p.l. iron.
 16. A process as described in claim 9wherein an oxygen partial pressure between about 2 atms. and 20 atms. isemployed.
 17. A process as described in claim 9 wherein themetathesis-leach-residue slurry is heated to a temperature between about80* C. and 125* C.
 18. A process as described in claim 9 whereiN themetathesis-leach-residue slurry is heated to a temperature between about100* C. and 110* C.
 19. A process as described in claim 9 whereinoxygen, partial pressures of at least about 5 atms. are employed.
 20. Aprocess for recovering nickel, copper and sulfur from materialscontaining the same which comprises providing a starting material in thedrastically quenched state and having a nickel to copper ratio greaterthan about 1:2 and a copper to sulfur ratio greater than about 4:1;treating the drastically quenched material with carbon monoxide partialpressures at least about 5 atms. and less than about 100 atms. at atemperature between about 50* C. and 200* C. to form substantially purenickel carbonyl and to provide a carbonylation residue; forming a slurryof the carbonylation residue with an acidic aqueous solution, whichsolution contains copper sulfate in amounts at least aboutstoichiometrically equivalent to the nickel contained in thecarbonylation residue and sulfuric acid in amounts sufficient tomaintain the solution at a pH value below about 5; heating thecarbonylation residue slurry to a temperature between about 100* C. and250* C. to leach the nickel therefrom by metathesis, to thereby producea metathesis-leach solution containing nickel and ametathesis-leach-residue containing substantially all the copper;recovering nickel from the metathesis-leach solution; forming a slurryof the metathesis-leach-residue with an aqueous sulfuric acid-ironsulfate leach solution containing at least about 2 g.p.l. iron andsulfuric acid at least stoichiometrically equivalent to the copper inthe metathesis-leach-residue; heating the metathesis-leach-residueslurry to a temperature between about 80* C. and 150* C. under oxygenpartial pressures of at least about 2 atms. to produce a pregnant coppersulfate solution and to liberate elemental sulfur and recovering copperfrom the pregnant copper sulfates.
 21. A process for treating acopper-rich fraction of copper sulfide obtained from a slowly coolednickel-copper matte to recover copper, nickel and sulfur which comprisesforming a slurry of the copper-rich fraction with an acidic aqueoussolution, which solution contains copper sulfate in amounts at leastabout stoichiometrically equivalent to the nickel contained in thecopper-rich fraction and sufficient sulfuric acid to maintain thesolution at a pH value below about 5; heating the copper-rich slurry toa temperature between about 100* C. and 250* C. to leach nickel from thecopper-rich fraction by metathesis to thereby produce a metathesis-leachsolution containing nickel and a metathesis-leach-residue containingsubstantially all the copper; recovering nickel from the metathesisleach solution; forming a slurry of the metathesis-leach-residue with anaqueous sulfuric acid-iron sulfate leach solution containing at leastabout 2 g.p.l. iron and sulfuric acid at least stoichiometricallyequivalent to the copper in the metathesis-leach-residue; heating themetathesis-leach-residue slurry to a temperature between about 80* C.and 150* C. under oxygen partial pressures of at least about twoatmospheres to produce a pregnant copper sulfate solution and toliberate elemental sulfur; and recovering copper from the pregnantcopper sulfates.
 22. A process as described in claim 21 wherein thecopper-rich fraction contains cobalt and the precious metals, and cobaltis recovered from the metathesis-leach solution containing nickel whilethe precious metals are recovered from the elemental sulfur.